Most spinal fusions are performed for patients with back pain with or without radicular symptoms (radiating pain) or neurogenic claudication (pain with walking) caused by degenerative disc disease (spondylosis). Roughly 90% of all spine surgeries involve fusion. Over 465,000 spinal fusions were performed in 2011 in the US at a cost of nearly 13 billion dollars.
Not to be limited by theory, pain from such pathology is believed to be caused by abnormal motion (instability). Fusion is performed to reduce or eliminate the motion of the degenerated disc segment by immobilizing the adjacent vertebral bodies. The majority of spinal fusions are performed with a posterolateral approach with bone graft material placed across the facets, lamina and transverse processes. A combination of transpedicular screws and connecting rods or plates provide immobilization of the vertebra until the bone graft material can form a solid bony fusion mass. A growing number of fusions are performed with an anterior approach with the bone graft placed in the disc space to allow bony fusion of the vertebral bodies across the disc space. Anterior fusions are typically performed in conjunction with posterolateral fusion rods to provide the immobilization needed for the bony fusion across the disc to occur. Bony fusion may take 6-12 months and fusion failure rates of 10-40% are reported in the literature.